Fractionation of tall oil



Patented Nov. 6, 1945 Arthur W. Hixson, Leonia, N.

New York, N. Y., Foundation, aware J., and Ralph Miller,

assignors to The Chemical Incorporated, acorporation of Del- No Drawing.Application April 25, 1940,

. Serial No. 331,602

Claims.

This invention is concerned with the fractionation of tall oil.

Tall oil is composed principally of rosin acids and fatty acids. Themost valuable part of tall oil is its fatty acid content. In ourcopending application Serial No. 264,780, filed March 9, 1939, U. S.Patent 2,247,496, a process of refining and fractionation of tall oilhas been described. The method outlined therein is particularlyapplicable to a batch process. We have discovered that the fatty acidcontent of tall oil can be separated from the other constituents in acontinuous process using liquefied, normally gaseous, hydrocarbons. Theadvantages of the present process are that it makes possible economiesin heat'and equipment as well as increasing the yield of substantiallypure fatty acids.

The fatty acids are extracted from crude tall oil by liquefied, normallygaseous, hydrocarbons at temperatures such that only fatty acids aresoluble in the hydrocarbon solvent. The extraction is most economicallycarried out in a continuous counter-current manner. Crude tall oil isintroduced at one end of the extraction system and a liquefied, normallygaseous, hydrocarbon introduced at the other end of'the extractionsystem. A solution of fatty acid dissolved in the liquefied, normallygaseous, hydrocarbon is withdrawn from one end of the system and aliquid composed primarily of rosin, in which some of the liquefied,normally gaseous, hydrocarbon is dissolved, is withdrawn from the otherend. The simplest type of contacting equipment such as a packed towercan be employed. Crude tall oil which has been preheated to the propertemperature is introduced close to the top of the tower. A liquefied,normally gaseous, hydrocarbon is introduced close to the bottom of thetower. The

hydrocarbon solution of fatty acids is withdrawn from the top of thetower while a liquid composed principally of rosin, in which a smallpercentage of the liquefied, normally gaseous, hydrocarbon is dissolved,is withdrawn from the base of the tower.

The temperature at which the extraction is carried out is a function ofthe composition of the olvent employed and the ratio of volume of talloil treated to volume of solvent used. If it is desirable, a temperaturegradient can be maintained between the two ends of the extractionsystem. In counter-current processes of this type, it is desirable thatthe two immiscible liquids be as fluid as possible and differ widely. indensity. As the tall oil is a very viscous material at room (oi.zoo-47.5)

temperature, it is desirable to operate at elevated temperatures. Forthis reason, propane is the preferred solvent. When propane is employed,a. temperature of about C. is used. Rosin is substantially insoluble inliquidv propane at 90 0.,

while the fatty acids present in tall oil are co pletely miscible withpropane at 90 C. If a mixture of hydrocarbons is employed, the besttemperature will be a function of the composition 'of the solvent.

If a mixture of propane and ethane is used, a. lower temperature ismaintained during the extraction than is used when propane is employedalone. If butane or isobutane is employed, the temperature must beraised for optimum results. Any combination of liquefied, normallygaseous, hydrocarbons can be used.

If a temperature radient is maintained, the high temperature end of thesystem is that at which the fatty acid solution leaves the system. Whena temperature gradient is employed, a condition exists that is similarto reflux in a distillation. The same advantages that accrue from theuse of reflux in a distillation can be obtained by use of a temperaturegradient. Any undesirable material that dissolves in the hydrocarbonphase at the cold end of the system precipitates at the hot end of thesystem. This permits the amount of solvent that must be circulated tofractionate a. given quantity of tall oil to be reduced.

Because of the enormous difference in volatility between the solventsemployed and tall oil, the solvent present in each phase isconveniently, readily and inexpensively separated from each phase bydistillation. The solvent is then returned to the extraction step.Because the solvent is so easily recovered, the process is operated withvery low solvent losses.

The products of this process are substantially pure fatty acids, securedin yields that are almost quantitative, and rosin containing all theother constituents of tall oil except the fatty acids.

We claim:

1. The process of extracting fatty acids from tall oil by contactingsame with a liquefied, normally gaseous, hydrocarbon at elevatedtemperatures at which the rosin is insoluble in the liquefiedhydrocarbons in a continuous counter-current system, continuouslywithdrawing from said.

system one liquid phase consisting essentially of fatty acids dissolvedin the liquefied hydrocarbon and a second phase consisting essentiallyof liquid rosin containing some dissolved hydrocarbon.

2. The process of extracting fatty acids from tall oil comprisingsubjecting said oil to a mixture of liquefied, normally gaseous,hydrocarbons at elevated temperatures of the order of 90 C. sufflcientlyhigh to distribute the fatty acids and the rosin respectively into twoliquid phases in a continuous counter-current relation.

3. A process in accordance with claim 1 in which the solvent is propaneand in which the temperature in the system is maintained about 90 C.

4. A process of treating tall oil and recovering a' fatty acid fractionand a rosin fraction therefrom which comprises passing preheated talloil to the upper section of a continuous countercurrent extractiontower, counter-currently passing liquid propane at a temperature ofsubstantially 90 C. into the lower section of said tower; continuouslywithdrawing from the upper portion of the tower a liquid fractionconsisting of fatty acids dissolved in propane and continuouslywithdrawing from the lower end of the system a liquid rosin fractioncontaining some dissolved propane. 5. A process in accordance with claim4 in which the two withdrawn fractions are separately treated to recoverthe contained propane and recycling the recovered propane for furtherextraction of tall oil.

ARTHUR W. HIXSON.

RALPH MILLER.

